Shared storage using either a storage area network (SAN) or network attached storage (NAS) device enables many key features of the virtual server environment, such as virtual machine (VM) migration, distributed resource management and site recovery management. As a result it’s often thought that the hard work of implementing, maintaining, tuning and upgrading a SAN is worth the effort. But what if the benefits of virtualization could be realized without going to a SAN at all? Such a ‘SAN-less’ infrastructure can now be created that provides the benefits of a SAN, even adding enhanced performance and availability, while minimizing network complications.

What is a Flash-only, SAN-less Virtual Infrastructure?

A SAN-less virtual infrastructure eliminates the need for hosts to connect to a dedicated shared storage pool, yet provides all the capabilities of a SAN. The storage is local to the host and data sharing is host-to-host, instead of host-to-SAN. And, this storage is PCIe SSD Flash for maximum performance. To provide high availability and to support data movement it leverages VMware Fault Tolerance (FT) which provides 100% uptime to virtual machines even if there is an unexpected hardware failure.

The Benefits of Flash-only, SAN-less Designs

Benefit # 1 - Maximum Flash Performance

Flash based storage is often considered the “go to” option when performance of the virtual environment becomes a challenge. The problem is deciding where in the storage infrastructure to make that investment. For SAN environments, the complexities of SAN architectures are made more difficult as storage administrators try to maximize the performance capabilities of Flash. With Flash in the mix networking configurations that were not a bottleneck before are exposed by the zero latency Flash technology.

Vendors make this even more complicated by “bolting” Flash onto existing SAN architectures and then using complex caching or tiering software to move ‘hot’ data to the high speed devices. These solutions are acceptable until there is a cache miss. Even if enough Flash can be purchased to make sure that misses are rare, the complexity of removing bottlenecks from the storage network remains, and of course costs go up.

To solve the networking challenges some virtual environments have considered PCIe SSD Flash solutions that install in the server and typically cache data locally. While this removes some of the challenges of fine tuning the storage network, the concern about cache misses remains. And, there is the added challenge of coordinating cache management with the underlying hypervisor.

Companies like OCZ Technology have introduced a Flash-only solution that leverages PCIe SSD Flash cards but uses those cards for storage of the entire virtual machine. As a result there is no risk of a cache miss. Data is synchronously written to another host with a PCIe SSD for data protection and high availability via a simple, private 10GbE network. The result is that data is fast, local and extremely well protected.

Benefit # 2 - Maximum Application Availability

In the SAN-Less Flash-only design availability is actually better than in the traditional SAN environment. As mentioned above data is synchronously written from a VM on one host to a shadow VM on a target host. Traditional migration of VMs is fine for planned outages but are not acceptable for hard failures. Leveraging VMware FT in combination with Flash Virtualization and Mirroring capabilities provides data protection and application availability when an unplanned failure occurs. While less frequent, these failures can be more severe, with the threat of data loss and the associated business impact.

With software like OCZ’s VXL Virtualization with built in Flash mirroring support for FT if a failure occurs the shadow VM takes over within 20-30 seconds of the first failure. FT provides protection from VM lock up and also physical host failure. In both cases no data is lost, and as soon as the FT process realizes that the original VM is down, the application picks up right where it left off.

Benefit # 3 - Maximum Simplicity

It is not uncommon for virtualized environments with a SAN as their supporting infrastructures to require that administrators spend hours per week tuning the performance of that environment. In fact many enterprises have begun to consider a full time storage performance specialist just to keep the virtual environment running at expected levels of performance and utilization. This requirement, at a minimum, stretches already thin IT staffs even thinner and at a maximum increases the cost of supporting the virtualized infrastructure, thereby reducing its ROI.

The net impact of the SAN-less, Flash only infrastructure is that the virtual environment becomes significantly simpler to manage on a day to day basis. All data is on PCIe SSD Flash inside the servers so there’s nothing left to tune. And, there is no fear of the performance impact of a cache miss since all the data is on SSD, which the CPU has direct internal access to via the PCIe bus. Even the networking is simplified. Other than the private 10GbE network for shadow VM synchronization there is no network to constantly monitor and tune.

Benefit # 4 - Maximum Price for Performance

A natural assumption is that the price of putting PCIe SSD Flash inside every server has to be too expensive to be practical. In reality this may not be. There is a significant savings in SAN infrastructure (switches and cards) as well as a the obvious savings in the actual SAN storage hardware. In addition many environments should realize a significant reduction in power and cooling costs with this architecture.

Bonus Benefit - Extending the Life of the SAN

For many environments that already have an investment in a SAN or a NAS, the SAN-less, All-Flash architecture is an ideal refresh option. Instead of buying a new storage system, they can leverage the existing one, changing its focus to a capacity centric operation, designed to store older VMs and their data. Implementing OCZ VXL Virtualization with FT support as the “SAN refresh” can accomplish this. Once the card and software are installed, users can leverage a capability like Storage Vmotion to migrate the most active VMs to the PCIe Flash storage in their respective hosts. This gives these production VMs a massive performance boost as well as a new level of availability. It also lessons the load on the legacy storage system.

Summary

A SAN-less, All-Flash solution eliminates the complexity inherent in most shared storage architectures, especially shared storage with Flash. It also overcomes a common problem of traditional PCIe SSDs by providing data and application availability and eliminating concerns of cache management. In one step it reduces complexity and removes the big problems of performance and availability.